The objective of the research project is to investigate the functional significance of some genetically-associated variations in morphology that occur within Ammon's horn (hippocampus and area dentata) in house mice. Specifically, we are determining some of the behavioral consequences of naturally-occurring variations in neuronal connectivity and variations that are connectivity-related. Variations under study include an alteration in the distribution of granule cell synapses upon pyramidal cell dendrites of hippocampal regio inferior, and variations in number of: (a) granule cells in area dentata and of (b) pyramidal cells of hippocampal regio superior and regio inferior. Studies designed to characterize the variations include descriptive morphological surveys and developmental and genetic analyses. These studies are followed by mating programs designed to produce groups of morphologically extreme mice for behavioral testing. The behavioral testing program is designed to investigate behaviors that are theoretically under the control of Ammon's horn, especially those that have been shown experimentally to be differentially associated with its various subdivisions. The results of the project are expected to lead to a better understanding of the morphological and functional organization of Ammon's horn and of the adaptive significance of genetically-associated variation in this organization.